356 CHEMICAL ENGINEERING
to note distilled water is used in washing refined sugar to keep down the ash.) The wash need not be great since the ratio of water to solids is so very small. Where the product is subject to bacterial action but not affected by moderate heat, a centrifuging with steam both washes and sterilizes.
Wet Grinding.—Dissolution by grinding the solids in the solvent is a method seldom used in the chemical world but almost invariably in the metallurgical world on like problems. Where the solvent is neutral or non-corrosive the dissolution can be greatly accelerated by wet grinding at no greater cost. It offers distinct advantage in reducing dust and also offers great possibilities in lowering the cost of grinding.
Conclusion.—It is impossible to make any definite statement as to which of the various types of dissolution apparatus is to be regarded as the best due to the fact that each particular industry offers special problems and each material must be handled in a slightly different manner. However, it is perfectly evident that the chemical industry is reaching a point where it is necessary to introduce labor and power-saving machinery where in the past tonnages had not warranted it, and the process of dissolution and washing being a process which is practically universal among chemical plants will undoubtedly be studied and new machinery Leveloped which will further increase its efficiency.